Turbulent structure in water under laboratory wind waves     

Ikuo Yoshikawa  Hiroshi Kawamura  Kuniaki Okuda  Yoshiaki Toba 《Journal of Oceanography》1988,44(3):143-156

The structure of the turbulent boundary layer underneath laboratory wind waves was studied by using a combination of a high-sensitivity thermometer array with a two-component sonic flowmeter. The temperature fluctuations are used to detect movements of water parcels, with temperature as a passive quantity. The turbulence energy was dominant in the frequency range (0.01 0.1 Hz), which was much smaller than the wind-wave frequency (2 5 Hz), and in which the turbulence was anisotropic. There was a frequency range (0.2 2 Hz for velocity, 0.2 5 Hz for temperature fluctuation) where the turbulence was isotropic and had a –5/3 slope in the energy spectrum. These points are the same as those in previous works. However, by analyses of the time series by using a variable-interval time-averaging technique (VITA), it has been found that conspicuous events in this main turbulence energy band are the downward bursting from the vicinity of the water surface. Thus the structure of the water layer underneath the wind waves has characters which are similar to the familiar turbulent boundary layer over a rough solid wall, as already conceived. It has been found that, at the same time, the turbulence energy can be related to quantities of the wind waves (the root mean squared water level fluctuation and the wave peak frequency), for different wind and wave conditions. That is, the turbulence underneath the wind waves develops under a close coupling with the wind waves.  相似文献   

Acceptance of the 2001 V. M. Goldschmidt award     

Ikuo Kushiro 《Geochimica et cosmochimica acta》2002,66(4):551-552

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On the lateral variations in chemical composition and volume of quaternary volcanic rocks across Japanese arcs     

Ikuo Kushiro 《Journal of Volcanology and Geothermal Research》1983,18(1-4)

The Fe/Mg+Fe) ratios (X_Fe) of the Quaternary basalts (SiO₂ < 53 wt.%) in the Japanese arcs were examined. The X_XFe of relatively magnesian basalts decreases from the volcanic front toward the Japan Sea across the arcs. Based on the partition coefficient of Mg-Fe²⁺ between olivine and liquid, it is suggested that all the basalts near the volcanic front, which are mostly tholeiitic basalts, are significantly fractionated, whereas many basalts near the Japan Sea, which are mostly alkali basalts, are little fractionated. The K₂ O content in the primary basalt magmas increases toward the Japan Sea. Combining the X_Fe and K₂ O data, it is suggested that relatively large amounts of tholeiitic magmas are produced near the volcanic front, but they fractionate during their ascent, whereas smaller amounts of alkali basalt magmas are formed near the Japan Sea, but they can ascend with less fractionation. The density of primary tholeiite magma is significantly larger than that of primary alkali basalt magmas. It is most likely that primary tholeiite magmas cannot ascend beyond the upper crust and would fractionate to produce less dense tholeiitic magmas near the volcanic front, whereas primary alkali basalt magmas can ascend through the upper crust without fractionation, as far as buoyancy is the principal ascending force. In the Japanese arcs, the stress field may be less compressional near the Japan Sea than near the volcanic front, so that magmas can ascend more rapidly in the latter region than in the former. These two factors may be responsible for the above mentioned chemical variations of basalt magmas across the arcs. The variation in volume of the Quaternary volcanic rocks across the arcs can be explained by the presence of a melt-rich zone above but nearly parallel to the subducted slab.  相似文献   

Effect of pressure on the diffusivity of network-forming cations in melts of jadeitic compositions     

Ikuo Kushiro 《Geochimica et cosmochimica acta》1983,47(8):1415-1422

The diffusivities of network-forming cations (Si⁴⁺, Al³⁺, Ge⁴⁺ and Ga³⁺) in melts of the jadeitic composition NaAl(Si, Ge)₂O₆ and Na(Al, Ga)Si₂O₆ have been measured at pressures between 6 and 20 kbar at 1400°C. The rates of interdiffusion of Si⁴⁺-Ge⁴⁺ and Al³⁺-Ge³⁺ increase with increasing pressure at constant temperature. The results are consistent with the ion-dynamics computer simulations of Jadeite melt by Angellet al. (1982, 1983). The coefficient measured for the Si⁴⁺-Ge⁴⁺ interdiffusion is between 8 × 10^?10 and 2.5 × 10^?8$\text{cm}{}^2\text{sec}$ at 6 kbar, depending on the composition of the melt, whereas at 20 kbar it is between 7 × 10^?9 and 2 × 10^?7$\text{cm}{}^2\text{sec}$. The effect of pressure is greater for more Si-rich compositions (i.e., closer to NaAlSi₂O₆ composition). The coefficient measured for the Al³⁺-Ga³⁺ inter- diffusion is between 9 × 10^?10 and 3 × 10^?9 cm²/sec at 6 kbar and between 3 × 10^?9 and 1 × 10^?8$\text{cm}{}^2\text{sec}$ at 20 kbar. The rate of increase in diffusivity with pressure of Al³⁺-Ga³⁺ (a factor of 3–4) is smaller than that of Si⁴⁺-Ge⁴⁺ (a factor of 7–17).The Si⁴⁺-Ge⁴⁺ interdiffusion in melts of Na₂O · 4(Si, Ge)O₂ composition has also been measured at 8 and 15 kbar for comparison. The effect of pressure on the diffusivity in this melt is significantly smaller than that for the jadeitic melts. The increase in diffusivity of the network-forming cations in jadeitic melts with increasing pressure may be related to the decrease in viscosity of the same melt. The present results, as well as the ion-dynamics simulations, suggest that the homogenization of partial melts and mixing of magmas would be more efficient at greater depths.  相似文献   

Compositional relations of coexisting orthopyroxene,pigeonite and augite in a tholeiitic andesite from Hakone Volcano     

Yasuo Nakamura  Ikuo Kushiro 《Contributions to Mineralogy and Petrology》1970,26(4):265-275

The compositions of five different coexisting pyroxenes hypersthene, pigeonite and augite in groundmass and bronzite and augite of phenocryst in a tholeiitic andesite from Hakone Volcano, Japan have been determined by the electron probe microanalyser. It is shown that there is a compositional gap of about 25 mole per cent CaSiO₃ between groundmass pigeonite and augite, compared with 35 per cent CaSiO₃ between phenocrystic augite and bronzite. Subcalcic augite or pigeonitic augite was not found. The groundmass augite, which occurs only as thin rims of pigeonite and hypersthene, is less calcic and more iron-rich than the phenocryst augite. It is also shown that the groundmass pigeonite is 3–4 mole per cent more CaSiO₃-rich than the coexisting groundmass hypersthene. The Fe/(Mg + Fe) ratios of these coexisting hypersthene and pigeonite are about 0.31 and 0.33, respectively. It is suggested from these results that a continuous solid solution does not exist between augite and pigeonite of the Fe/(Mg + Fe) ratio at least near 0.3 under the conditions of crystallization of groundmass of the tholeiitic andesite. It is suggested from the Mg-Fe partition and the textural relation that the groundmass augite crystallized from a liquid more iron-rich than that from which groundmass hypersthene and pigeonite crystallized.  相似文献   

Pressure dependence of nickel partitioning between forsterite and aluminous silicate melts     

Bjørn O. Mysen  Ikuo Kushiro 《Earth and Planetary Science Letters》1979,42(3):383-388

Nickel partitioning between forsterite and aluminosilicate melt of fixed bulk composition has been determined at 1300°C to 20 kbar pressure. The value of the forsterite-liquid nickel partition coefficient is lowered from >20 at pressures equal to or less than 15 kbar to <10 at pressures above 15 kbar.Published data indicate that melts on the join Na₂O-Al₂O₃-SiO₂ become depolymerized in the pressure range 10–20 kbar as a result of Al shifting from four-coordination at low pressure to higher coordination as the pressure is increased. This coordination shift results in a decreasing number of bridging oxygens in the melt. It is suggested that the activity coefficient of nickel decreases with this decrease in the number of bridging oxygens. As a result, the nickel partition coefficient for olivine and liquid is lowered.Magma genesis in the upper mantle occurs in the pressure range where the suggested change in aluminum coordination occurs in silicate melts. It is suggested, therefore, that data on nickel partitioning obtained at low pressure are not applicable to calculation of the nickel distribution between crystals and melts during partial melting in the upper mantle. Application of high-pressure experimental data determined here for Al-rich melts to the partial melting process indicates that the melts would contain about twice as much nickel as indicated by the data for the low-pressure experiments. If, as suggested here, the polymerization with pressure is related to the Al content of the melt, the difference in the crystal-liquid partition coefficient for nickel at low and high pressure is reduced with decreasing Al content of the melt. Consequently, the change ofD_Ni^{ol-andesite melt} is greater than that ofD_Ni^{ol-basalt melt}, for example.  相似文献   

SHRIMP U–Pb zircon dating of quartz-bearing eclogite from the Sanbagawa Belt, south-west Japan: implications for metamorphic evolution of subducted protolith     

Kazuaki Okamoto  Hironao Shinjoe  Ikuo Katayama  Kentaro Terada  Yuji Sano  Simon Johnson 《地学学报》2004,16(2):81-89

In order to decipher the origin of eclogite in the high‐P/T Sanbagawa metamorphic belt, SHRIMP U–Pb ages of zircons from quartz‐bearing eclogite and associated quartz‐rich rock (metasandstone) were determined. One zircon core of the quartz‐rich rock yields an extremely old provenance age of 1899 ± 79 Ma, suggesting that the core is of detrital origin. Eight other core ages are in the 148–134 Ma range, and are older than the estimated age for trench sedimentation as indicated by the youngest radiolarian fossil age of 139–135 Ma from the Sanbagawa schists. Ages of metamorphic zircon rims (132–112 Ma) from the quartz‐rich rock are consistent with metamorphic zircon ages from the quartz‐bearing eclogite, indicating that eclogite facies metamorphism peaked at 120–110 Ma. These new data are consistent with both the Iratsu eclogite body and surrounding highest‐grade Sanbagawa schists undergoing coeval subduction‐zone metamorphism, and subsequent re‐equilibration under epidote amphibolite facies conditions during exhumation.  相似文献   

Key word Index     

Ikuo Towhata 《Geotechnical and Geological Engineering》2004,22(4):650-650

Other Index

Key word Index  相似文献   

Simulation analyses of buildings damaged in the 1995 Kobe,Japan, earthquake considering soil–structure interaction     

Yasuhiro Hayashi  Kazuo Tamura  Masafumi Mori  Ikuo Takahashi 《地震工程与结构动力学》1999,28(4):371-391

A series of studies was conducted on three buildings of steel reinforced concrete structures with RC shear walls damaged in the 1995 Hyogo-ken Nanbu earthquake. These buildings are located in an area where structural damage centred around. Two of these buildings suffered severe damage, while the third was not structurally damaged. Our studies deal with site inspections, including micro-tremor measurement of buildings, the evaluation of input motions, and the response analyses considering soil–structure interaction. The results of simulation analyses of the two severely damaged buildings correspond to their actual damage state. From the response analyses of the one slender building with no structural damage, it was concluded that uplifting is the main reason it did not suffer any structural damage. Through these studies, the importance of soil–structure interaction and effective input motion is fully understood. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

Interannual variability of the Kuroshio transport passing through the 137°E meridian in an OGCM related to the North Pacific windstress     

Yoshinobu Wakata  Takashi Setou  Ikuo Kaneko  Hiroshi Uchida  Shiro Imawaki 《Journal of Oceanography》2006,62(1):25-35

The interannual variability of the Kuroshio volume transport passing through the 137°E meridian south of Japan was simulated with an ocean general circulation model (OGCM). The time series of the Kuroshio volume transport over the 1000 m depth in the OGCM is well reproduced by the one-dimensional quasi-geostrophic (QG) vorticity equation with a windstress forcing. In our analysis of the OGCM and QG results, we found that peaks and troughs of the time series of the Kuroshio volume transport with 2–3 yr time-scale were induced by windstress curl, both local and immediately eastward, whereas longer time-scale variability was also induced by windstress curl near the dateline.  相似文献